This invention in general relates to connectors for coupling optical fibers and more particularly to apparatus for testing the optical throughput or efficiency of beam-expansion type lens structures utilized in connecting optical fibers.
As is well-known, fiber optical links have the same basic elements found in electrical communications systems. A transmitter converts electrical signals into light signals which are transmitted through optical fibers to a receiver where light signals are converted back to electrical ones. In the link, connectors serve to assure that tight physical or optical contact is made and maintained between the optical fibers and the transmitting or receiving components of the system.
Although seemingly simple, making the connection between the components of a fiber optic link is extremely troublesome and very different from making an electrical connection which requires only a reliable physical contact between two conductors. For a proper connection between optical fibers, the ends of the fibers must be accurately aligned to assure that light leaves and enters them within a certain range of angles. If not, leakage occurs causing large signal losses which make an otherwise attractive communication link impractical.
To solve the connector problem with tolerable losses, those skilled in the art have developed a class of connectors referred to as expanded beam or imaging connectors which are of the sort described in, for example, U.S. Pat. Nos. 4,183,618 and 4,186,995 and in an article entitled "Connectors that stretch" appearing in October 1980 in Optical Spectra.
The essence of the expanded-beam type connector is to enlarge and collimate or roughly collimate the light beam which emerges from the input fiber or fibers which are accurately placed in one-half of the connector at or nearly at the focus of its lens. The other half of the connector, similar in design but which may in fact be scaled to be larger, then acts in reverse by taking the expanded input beam and focusing it into the output fiber end located at or nearly at the axial focus of the other connector half. In this manner the task of optical alignment becomes one of mechanically aligning relatively large beam cross-sections rather than small fiber ends as is done in strictly mechanical connectors.
With such connectors, however, the burden on optical performance and related mechanical geometry is great and must be verified in a reliable manner consistent with usage to assure high quality.
It is thus a primary object of the present invention to provide apparatus and methods by which the performance and mechanical integrity of expanded beam type connectors for use in coupling optical fibers can be accurately and reliably tested.
It is another object of the present invention to provide apparatus and methods by which the optical efficiency of expanded-beam type connectors can be tested in a manner consistent with their usage.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention, accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts exemplified in the following detailed disclosure and the methods attendant to the use of the apparatus.